(A) Field of the Invention
The present invention is related to an over-current protection device and manufacturing method thereof, more specifically, to an over-current protection device with high thermal dissipation and manufacturing method thereof.
(B) Description of the Related Art
For the present broad application of portable electronic products, such as mobile phone, notebook, portable camera, and personal digital assistant (PDA), the use of over-current protection devices to prevent the short circuit caused by an over-current or over-heating effect in a secondary battery or circuit device is becoming more and more important.
The resistance of a positive temperature coefficient (PTC) conductive material is sensitive to temperature variation, and can be kept extremely low at normal operation due to its low sensitivity to temperature variation so that the circuit can operate normally. However, if an over-current or an over-temperature event occurs, the resistance will immediately increase to a high resistance state (e.g., above 104 ohm.) Therefore, the over-current will be reversely eliminated and the objective to protect the circuit device can be achieved.
As shown in FIG. 1, a conventional over-current protection device 10 comprises a PTC material layer 101, two electrode layers 102, two isolation layers 103, two conductive bars 104 and two soldering electrode layers 105. The soldering electrode layers 105 are overlaid on the electrode layers 102 which are overlaid on the upper and lower surfaces of the PTC material layer 101. The two electrode layers 102 and two soldering electrode layers 105, over and under the PTC material layer 101, are electrically connected to each other by means of the conductive bars 104 through the PTC material layer 101 and two electrode layers 102. The isolation layer 103 separates the electrode layer 102 into right and left portions which are isolated from each other. Therefore, the over-current protection device 10 has two right and left electrical terminals, and leads (not shown) are employed to separately connect them with a circuit or a device which needs to be protected.
The current trend is towards miniaturizing electrical apparatuses, hence the thermal dissipation of the electrical device becomes more important for consideration to design parameters. If heat energy cannot be effectively dissipated, the lifetime and reliability of the over-current protection device are degraded.